JP2001-082204A published in the year 2001 by the Japan Patent Office proposes to cut down fuel supply, namely cut fuel to the engine from a fuel supply device to economize vehicle fuel consumption when a vehicle internal-combustion engine is forced to rotate faster than a predetermined rotation speed due to the inertial force of the moving vehicle, namely in an engine braking state. If an engine rotation speed falls below a predetermined rotation speed due to the fuel cut, fuel supply is resumed.
Among vehicles configured to connect the engine and the transmission via a torque converter, there is a vehicle that allows the lockup clutch to directly connect the engine and the transmission in response to a running condition, so as to suppress fuel consumption.
If the above prior art is applied to such a vehicle and fuel supply is resumed with the lockup clutch being in an engaged state, an output torque of the engine rapidly increases and is directly transmitted to the transmission via the lockup clutch due to resume of fuel supply, namely a torque shock called a recovery shock is generated, thereby imposing discomfort on a driver and a passenger(s).
If the lockup clutch enters a disengaged state at a faster engine rotation speed than that needed for resuming fuel supply, the lockup clutch does not perform torque transmittance when fuel supply is resumed. A recovery shock does not generate since fluid in the torque converter absorbs changes in the torque.